1. Field of the Invention
This invention relates to abrasive articles and to their preparation. In particular, the invention relates to abrasive sheet materials having a layer of pressure-sensitive adhesive for attachment of the abrasive sheet to the back-up pad of a sanding implement.
2. Background Art
Abrasive sheet materials comprising a substrate, e.g., paper, having a first major surface bearing an abrasive layer and a second major surface having a layer of pressure-sensitive adhesive thereon are known. The abrasive sheets are generally in the form of rectangles or circular discs and the pressure-sensitive adhesive is used to attach the abrasive sheet to the back-up pad of a sanding implement, e.g., a rotary or orbital sanding device. When such abrasive sheets are manufactured it is common practice to protect the pressure-sensitive adhesive layer with a liner in order to prevent the adhesive from becoming contaminated. The liners generally comprise a plastic film or paper which may be treated with a release material, e.g., a silicone.
The process of manufacturing such abrasive articles generally comprises forming a web comprising a substrate having a first major surface bearing an abrasive layer and the second major surface having a layer of pressure-sensitive adhesive and a protective liner covering the pressure-sensitive adhesive. Individual abrasive articles are then cut from the web. The abrasive articles may have any desired shape but are generally rectangular or circular. The cutting operation generally results in the abrasive and liner having perimeters which are coterminous, i.e., the cutter simultaneously cuts the abrasive substrate and liner.
One of the problems associated with abrasive articles manufactured in such a manner is that it is difficult for the user to peel the protective liner from the pressure-sensitive adhesive. This problem arises because it is difficult for the user to separate an edge of the liner from the adjacent edge of the abrasive material. Once an edge has been separated it is easy to peel the liner away from the adhesive.
This problem has been overcome by providing the liner with a lift flap or finger lift. One method of providing a lift flap comprises adhering a circular tab to the outer surface of the liner in such a manner that it projects beyond the perimeter of the liner, the projecting portion being free of adhesive and providing a lift flap for removing the liner. Whilst this arrangement is effective from the point of view of the end user it involves the application of tabs to each individual abrasive article.
A second method of providing a lift flap comprises cutting the web of abrasive material and protective liner in such a manner that the perimeters of the abrasive material and liner are not coterminous and the perimeter of the liner extends beyond that of the abrasive material to define a lift flap. Again, this arrangement is satisfactory from the point of view of the end user but requires precisely controlled conditions of the cutting operation in order to cut the abrasive material in some regions without cutting the protective liner.
A further method of overcoming the problem is to cut the individual abrasive materials prior to application of the liner and to individually apply the abrasive materials to an oversized liner. For example, circular discs have been applied to a square liner. This process is not efficient and utilizes large amounts of protective liner.
DE-3844261A. published Jul. 5, 1990, discloses a reusable adhesive product and an abrasive or polishing article which is fixed on by adhesion having an underlay with a suitable top coating and pressure-sensitive adhesive layer on the other side. The adhesive layer has a peel-off composite consisting of a substrate and pressure-sensitive tacky layer on the under side; part of the adhesive layers have non-tacky segments for gripping purposes. The non-tacky grip areas, which enable the peel-off of the part to be removed are formed by interposing a strip of tabbing tape, e.g., a strip of release material, between the adhesive and the substrate at the edge of the abrasive material to provide a free edge for gripping by the user.
It is an object of the present invention to provide an alternative form of lift flap for use on the liner of abrasive articles.